Introduction. Mass vaccination, implemented in Russia within the framework of the Russia National Vaccination Calendar, is a key component in the fight against vaccine-preventable infections (measles, mumps, rubella). The aim. The study’s aim was to assess herd immunity to the most common vaccine-preventable infections in several Russian regions. Materials and methods. The study involved 18 247 volunteers from several regions (Amur, Irkutsk, Nizhny Novgorod, Kaliningrad) and the Republic of Crimea. During the study, participants completed a questionnaire. A cohort of volunteers, stratified by age (1–5, 6–11, 12–17, 18–29, 30–39, 40–49, 50–59, 60–69, ≥ 70 years), was randomized using a web application. Antibodies to the measles, rubella, mumps were quantitated by ELISA (IgG) using Russian-made test systems. Results. The cohort average seropositivity magnitude for measles, mumps, and rubella were 75.7%, 84.0%, and 95.8%, respectively. For measles, the highest seropositivity level was observed in the group 1–11 years (Me = 74.8%; IQR = 68.5–83.5) and the group 60–70+ years (95.1%; IQR = = 93.2–95.8). Regarding mumps, these two ago groups also showed peak values: 1–11 years (Me = 85.9%; IQR = 81.4–92.5) and 60–70+ years (Me = 88.6%; IQR = 83.7–90.6). The lowest measles seroprevalence was observed in 18–39-year age group (Me = 59.7%; IQR = 55.9–64.6). For mumps, the lowest seroprevalence was also observed in 18–39-year age group (Me = 78.4%; IQR = 63.9–83.7). Regarding rubella, seropositivity was evenly distributed across the entire cohort: Me = 95.8% (IQR = 93.9–97.5). Among specific vaccines for immunization against measles/mumps or rubella, the mumps-measles or live monovalent rubella vaccine, respectively, was most or more frequently used. Conclusion. High measles and mumps seroprevalence among children is due to post-vaccination immunity following mass immunization, primarily with the mumps-measles vaccine. Seroprevalence in older adults is associated with childhood infections that have elicited post-infectious immunity. Rubella immunity was virtually independent of age, geographic location, or climate factors. Reduced measles and mumps seropositivity among middle-aged individuals may lead to emergence of sporadic cases of these diseases, which may require additional measures, including catch-up vaccination.

Background/Objectives: In the Republic of Serbia, measles vaccination was first introduced in 1971, while combined vaccination (measles, mumps, rubella) was made mandatory in 1996 as part of the national vaccination program. Reported prevalence values for 2023 were <0.75 cases per 100K population for measles, 0.09 cases per 100K for mumps, and no cases of rubella. Methods: This cross-sectional study was performed in May, 2024 as part of the project "Herd Immunity to Vaccine-Preventable and Other Relevant Infections in the Belgradian Population." It focused on assessing herd immunity to measles, mumps and rubella (MMR) among residents insofar as these remain a public concern despite the availability of vaccines. A total of 2533 subjects were distributed across nine age groups, covering those aged 1-70+ years and various professional groups residing in Belgrade. Participants were stratified by age and activity. Upon obtaining individual information by online questionnaire and receiving a signed statement of informed consent, blood samples were obtained for IgG antibody testing (ELISA) to determine MMR serological status. The results were compared to national and international immunization standards to evaluate herd immunity levels. Results: Our results indicate varying levels of immunity for each virus, with specific demographic groups showing different immunity levels. Total measles seroprevalence during this study was 74.7%, with significant variation across all age groups. While high seropositivity was observed in both children (90.7%) and elder age groups (98.4%), middle-aged individuals in the age group 30-49 years showed significantly lower IgG levels. Between 2021 and 2023, there were no registered cases of rubella detected in Serbia, which indicates a high level of immunity. This was confirmed here with consistently high IgG levels across all age groups, with an average seropositivity of 94.8%. Average mumps seropositivity across all age groups was 85.1%. The lowest value was in the young child (1-5 years) age group (76.1%); the highest was in the elderly group (92.6%). Conclusions: The current findings suggest that the Belgradian population has strong overall immunity to MMR, yet with some concerns regarding measles immunity in middle-aged adults, suggesting a potential need for catch-up vaccinations. While rubella status indicates strong herd immunity and minimal risk of outbreaks, mumps immunity in some groups (children, middle-aged adults) is below the protective threshold. While it is still sufficient to prevent widespread transmission, it should be closely observed. To our knowledge, this study is the first of its kind to provide data about MMR seroprevalence in Belgrade. Findings indicate the need for constant surveillance and revaccination of vulnerable/seronegative groups.

Introduction. Specific prevention of vaccine-preventable infections (VPIs) has been the main prerequisite to radically lower their incidence in the Russian Federation. Since the Kherson Region joined the Russian Federation in 2024–2025, no VPI cases have been recorded, likely due to the level of herd immunity. The actual number of individuals immune to VPIs can only be estimated through serologically monitored herd immunity. Study objective was to assess herd immunity to measles, mumps, rubella, and diphtheria in specific Kherson Region districts. Materials and methods. The study involved 2.807 volunteers in seven municipal districts, aged 1 to 70+ years. A volunteer cohort, stratified by age (1–5, 6–11, 12–17, 18–29, 30–39, 40–49, 50–59, 60–69, ≥ 70), was randomized using the Web application. During the study, participants completed a questionnaire, IgG antibodies to specific agents (measles, mumps, rubella, diphtheria toxin) were measured in venous blood samples using ELISA test kits (Russia). Results. The average cohort seroprevalence for measles, rubella, mumps, and diphtheria among volunteers in the region were 83.4%, 95.1%, 65.7%, and 83.4%, respectively. Adults aged 18–29 years were the least protected against measles, rubella, and mumps, with the seropositivity: 70% for measles; 84.5% for rubella; and 44.6% for mumps. The most protected were people aged ≥ 50 years: 91.5–99.4% for measles; 98% for rubella; and 74.5–87.1% for mumps. People over 60 were the least protected against diphtheria (63.8–76.5%). In children’s groups, maximum seroprevalence was noted in the group aged 6–11 years: 90.8% for measles; 96.9% for rubella; 64.6% for mumps; and 90.4% for diphtheria. Most volunteers had low to moderate anti-measles and anti-diphtheria toxin IgG levels; and high anti-rubella IgG levels. The seropositivity of “naive” volunteers (those denying infection or vaccination) indicates insufficient laboratory VPI diagnostics in the Kherson Region. Conclusion. The level of herd immunity in the surveyed areas (Kherson Region) met the criterion for epidemiological well-being only with regard to rubella. Specifically, the percentage of seronegative individuals was below 10%. Insufficient seroprevalence for the measles and mumps viruses, as well as the C. diphtheriae, reflects conditions conducive for the spread of these infections among the population.

Specific measles, mumps, and rubella prevention has been the main prerequisite for a striking decline in the incidence of such infections in Russia. An increase in the percentage of seronegative individuals observed in recent years resulted in higher measles incidence being directly related to low herd immunity that accounts for a population protection solely under conditions of a high density of immunized individuals and their uniform distribution in the population. The number of immunized individuals may be estimated only while conducting seroepidemiological monitoring of herd immunity. The objective of the study was to assess a level of herd immunity in the St. Petersburg and Leningrad Region population against measles, mumps, and rubella viruses. Materials and methods. There were enrolled 6774 residents into the study: volunteers aged from 1 to 70+ years. The representativeness of the surveyed cohort was ensured by using the Web application “Monitoring of herd immunity against socially significant infections”, used at the stage of volunteer enrollment, by randomization and regulation of the sample size in age groups. Participants filled out a questionnaire and agreed to provide venous blood samples to assess IgG antibody levels against measles, mumps, and rubella viruses by using ELISA. Results. In September 2023, in St. Petersburg and the Leningrad Region, herd immunity met the criterion for epidemiological well-being only with respect to rubella. In all age groups, the proportion of seronegative individuals did not exceed 15%, and most volunteers had high Ab levels, both after illness and vaccination. For measles and mumps, the criterion for epidemiological well-being is considered not to exceed more than 7% seronegative individuals. A sufficient level of measles seroprevalence was detected only in older age groups (≥ 60 years old). Sufficient mumps seroprevalence was not detected in any age group. The average population (St. Petersburg, Leningrad Region) seroprevalence magnitude for measles, rubella, and mumps viruses were 81.4%, 95.5%, and 78.4%, respectively. The problematic age groups with low measles seroprevalence (62.4–74.3%) were adolescents (12–17 years) and young adults (18–39 years). Most seropositive individuals vaccinated against measles had low Ab levels; high levels were noted mainly in older measles convalescent individuals. Low mumps seroprevalence (~70%) was more often observed among adults aged 18 to 49 years. The distribution of seroprevalence in various occupational group was relatively uniform, with some predominance of seropositivity among pensioners and schoolchildren. Conclusion. The system of specific prophylaxis for vaccine-preventable viral infections used in Russia has shown high efficacy and contributed to the formation of herd immunity, which for many years allowed to lower a risk of both sporadic and group infections to minimal levels. Currently, measles and mumps seroprevalence in the local population is maintained at insufficient level to ensure epidemiological well-being. This necessitates making appropriate management decisions and conducting additional preventive measures aimed at enhancing relevant herd immunity.

Introduction. Rotavirus infection causes more than 250 million episodes of acute gastroenteritis annually, of which approximately 130,000 cases in children under 5 years of age are fatal. In this regard, the search for drugs for the treatment of rotavirus infection seems extremely relevant. The aim of the research was to evaluate the antiviral activity of Cytovir ® -3 against human rotavirus on a cellular infection model. Material and methods. The objects of the study were a mixture of active ingredients and individual components, identical in composition and ratio, contained in Cytovir ® -3. The study was carried out using a monkey kidney cell culture MA-104 and a laboratory strain of human group A rotavirus — 568, genotype G3P. Cultural, virological, molecular biological and statistical methods were used during the study. Results and discussion. Analysis of the survival of MA-104 cells in the presence of Cytovir ® -3 showed that in the concentration range from 100 to 200 µg/ml, the drug reproducibly exhibited antiviral activity, which was expressed in increased cell survival compared to the viral control. Cytovir ® -3 in a non-toxic concentration of 150 µg/ml suppressed the reproduction of rotavirus by 1.0-2.0 lg СC₅₀/ml with various schemes of introduction into cell culture at all periods of observation, which was accompanied by a significant decrease in the concentration of viral RNA and a cytoprotective effect.

Introduction. Due to the ability of the influenza virus to mutate, it is necessary to constantly search for new drugs with preventive and direct antiviral effects. The aim of the study is to investigate the protective antiviral properties of the drug Thymogen ® , a dosed nasal spray, on a model of lethal influenza pneumonia in laboratory animals. Material and methods. White mature mice were selected for the experiment on the antiviral activity of the tested drug samples against H1N1 influenza virus; the mice were divided into the following groups (30 animals each): two negative control groups; two groups receiving Thymogen ® , a dosed nasal spray (before and after infection); one group of animals received Tamiflu ® , and one received Hexoral ® . The mortality of animals with influenza pneumonia was assessed; histological and morphometric analyses were also carried out. Results and discussion. The morphological picture of the lungs of animals correlated with their protective activity when analyzing the survival of animals. The normalization of tissue structure was pronounced the most in the group of animals infected with the virus, pre-incubated with Thymogen ® , a dosed nasal spray, and in the group receiving Tamiflu ® . Moreover, the viral load in the lungs was lower by 1.5 and 1.2 orders of magnitude in the group receiving Thymogen ® , dosed nasal spray, compared to the negative control group (the 3 rd and the 6 th days of the experiment, respectively), which corresponds to a decrease in the intensity of viral reproduction by 31.6 and 15.8 times

Purpose of the study: to study the dynamics of developing herd immunity against SARS-CoV-2 in the population of the Republic of Kyrgyzstan during COVID-19. Materials and methods. The work was carried out using the methodology for assessing population immunity developed by Rospotrebnadzor (Russia) as well as the Ministry of Health (Kypgyzstan) and the St. Petersburg Pasteur Institute. The selection of participants was carried out by questionnaire using a cloud (Internet server) service. To monitor population immunity, a cohort of 2421 subjects was formed, who participated in all stages of seromonitoring. Volunteers were randomized according to age groups (1–17, 18–29, 30–39, 40–49, 50–59, 60–69, 70+ years), regional and professional factors. Antibodies (Abs) against SARS-CoV-2 nucleocapsid (Nc) and the receptor binding domain (RBD) of S-glycoprotein were determined by qualitative and quantitative methods. The study was carried out in 3 stages according to a single scheme: 1st stage — 06/28–07/03/2021, 2nd — 21–25/02/2022 and 3rd — 31/10–04/11/2022. Since 2021, Kyrgyzstan has been vaccinating the population against SARS-CoV-2 mainly using inactivated whole-virion vaccines. Results. Population immunity against SARS-CoV-2 was predominantly accounted for by both Ab types (Nc+RBD+). By the 3rd stage, the percentage of such persons reached 99.2%, Nc–RBD– volunteers — up to 0.8%. At the 1st stage, middle-aged people dominated, but age differences were leveled out by the 2nd stage. The greatest impact on seroprevalence was found among medical workers, the smallest — among businessmen and industrial workers. Populational vaccination significantly impacted on the state of herd immunity that reached 25% by the 3rd stage. The refusals of the population in Kyrgyz Republic from vaccination noted at the 2nd and especially 3rd stages did not significantly affect level of herd immunity, which could probably be associated with asymptomatic cases of COVID-19, against which primary vaccination had a booster effect. Conclusion. The dynamics of population humoral immunity against SARS-CoV-2 included a number of changes in the level of circulating antibodies (Nc, RBD), caused by both primary infection and vaccination. The herd immunity formed in population of Kyrgyzstan allowed to reduce the incidence of COVID-19 to almost sporadic level.

Background. The course of the COVID-19 epidemic process depends on population immunity which prevents pathogen spread. Aim: to study an evolution of SARS-CoV-2 humoral immunity in the Belarusian population rela- tive to COVID-19 pandemic dynamics. Materials and methods. The work was carried out according to a methodology for assessing herd immunity developed by Rospotrebnadzor (Russia) and the Belarusian Ministry of Health involving the St. Petersburg Pasteur Institute (SPPI) by taking into account the WHO recommendations. The study was approved by the Bioethics Committee of Belarus and the SPPI Bioethics Committee. Participant selection was carried out by ques- tionnaire using a cloud (internet server) service. To monitor herd immunity, a cohort of 4661 subjects (involved at all stages of seromonitoring) was formed from the total volunteer group. Study subjects were randomized into groups based on age (117, 1829, 3039, 4049, 5059, 6069, 70+ years), geographic region, and occupation. For the detection of antibodies (Abs) against SARS-CoV-2 nucleocapsid (Nc) and S glycoprotein receptor-binding domain (RBD), rel- evant assay systems were used according to the manufacturers instructions. A four-stage study was conducted according to a unified scheme. Results. At stage 1 (pandemic month 15), herd immunity was mainly accounted for by Nc+RBD+ Ab status alone. By stage 2 (4 months later), its specific proportion decreased by 1.2-fold, whereas percentage of subjects solely bearing RBD-specific Abs increased by 1.7-fold. At stages 3 and 4 (9 and 19 months after the onset) vs. stage 2, percent- age of subjects with RBD+Nc decreased by 3.5%; the proportion of persons with Nc+RBD Abs increased by 1.5-fold. The most important contributor in herd immunity turned out to be due to population vaccination, with coverage reaching 70% by stage 4. Among vaccines, compared with whole-virion, inactivated BIBP-CorV vaccine the Sputnik V and Sputnik Light vector were used most often. Conclusion. The evolution of herd SARS-CoV-2 humoral immunity included a series of changes in circulating Ab levels (Nc, RBD). The hybrid immunity formed helped to reduce the incidence of COVID-19 to sporadic level.

Despite all efforts of the world community, the COVID-19 pandemic remains one of the main epidemiological challenges of our time. Even with its widespread distribution, the infection may have certain local features due to social, geographic, and climatic factors. Objective: to study collective immunity to SARS-CoV-2 in the population of the Republic of Tajikistan.A cross-sectional, randomized study of herd immunity was carried out according to a program developed by Rospotrebnadzor and the St. Petersburg Pasteur Institute, taking into account WHO recommendations. The ethics committees of the corresponding entities approved the study: Tajik Ministry of Health and Social Protection; and the St. Petersburg Pasteur Institute (Russia). Based on questionnaire results, 4,022 people were selected, representing 0.15% (95% CI: 0.14-0.15) of the total population randomized by age and region. In subsequent laboratory analysis, 3682 people took part. The distribution and quantitative content of antibodies (Abs) to viral nucleocapsid (N Ag) and receptor binding domain (RBD Ag) were determined by ELISA. When questioned, a history of SARS-CoV-2 vaccination was indicated by 69.7% (95% CI: 68.2-71.2) of the volunteer cohort. Vector vaccines were most frequently used (50.6%; 95% CI: 48.7-52.5), with whole-virion inactivated preparations in second place (23.0%: 95% CI: 21.4-26.6) and mRNA vaccines in third place (21.0%; 95% CI:19.4-22.6).The cohort (n = 3682) featured 27.5% men and 72.5% women. The overall seroprevalence was 98.5% (95% CI: 97.7-99.2) in men and 99.4% (95% CI: 99.0-99.6) in women (differences statistically insignificant). Overall seroprevalence in the cohort was 99.2% (95% CI: 98.8-99.4) and ranged from 97.2 to 100% in certain subgroups. Asymptomatic seropositivity in the whole cohort was 98.4% (95% CI: 97.6-99.1). As a result of a mandatory vaccination program introduced in Tajikistan under a COVID-19 Emergency Project, the level of herd immunity among vaccinated individuals reached 99.5% (95% CI: 99.1-99.7), which is similar to the level reached in the cohort as a whole.The epidemic situation that developed in Tajikistan by mid-March 2022 was characterized by an almost absolute level of herd immunity, as evidenced by an absence of detected overt COVID-19 cases since the end of February (2022).

Introduction . The requirements of modern clinical guidelines for the treatment of respiratory viral infections suggest the possibility of identifying a specific viral pathogen. In this regard, the search for drugs with selective activity against respiratory syncytial virus and parainfluenza virus is relevant. The purpose of the work is to study the antiviral activity of the drug Cytovir®-3 in vitro in relation to the cytopathogenic effect of respiratory viruses (parainfluenza virus and respiratory syncytial virus). Material and methods . The antiviral effect of Cytovir®-3 in comparison with Umifenovir against parainfluenza virus and respiratory syncytial virus was studied on Vero cell culture. Drugs were administered 1 hour before (prophylactic regimen) and 1 hour after (treatment regimen) infection of the cell culture with respiratory viruses. The working range of concentrations of the studied drugs was calculated based on the values of 50% cytotoxic concentration calculated based on the results of a quantitative microtetrazole test. Results and discussion. The drug Cytovir®-3 in two schemes of application (therapeutic or prophylactic) showed its antiviral efficacy in vitro against respiratory syncytial virus and parainfluenza virus due in the non-toxic range (0–794 µg/ml). At the same time, the suppressive effect of the drug Cytovir®-3 against the parainfluenza virus begins at lower concentrations of the drug with its early (preventive) introduction into cell culture (250 mcg/ml). Conclusion . Antiviral activity of Cytovir®-3 has been proven in vitro against parainfluenza virus and respiratory syncytial virus. At the same time, in all series of experiments, Cytovir®-3 had a higher index of selectivity of antiviral action than that of the comparison drug Umifenovir.

Российская Федерация проводит последовательную работу по оказанию содействия странам - партнерам в наращивании научного потенциала и расширении сотрудничества в рамках изучения инфекционных заболеваний. В начале пандемии COVID-19, при поддержке Правительства Российской Федерации Роспотребнадзором была разработана многоэтапная программа серомониторинга иммунитета населения к SARSCoV-2, которая была реализована в Российской Федерации, Кыргызс кой Республике, Республике Беларусь, Республике Армения и Республике Таджикистан. В исследования включили разные возрастные и профессиональных групп перечисленных стран. У волонтеров оценивали уровни IgG антител к двум основным антигенам SARS CoV-2: нуклеокапсиду (Nc) и рецептор-связывающему домену S-белка (RBD) в силу их максимальной представленности во время инфекционного или поствакцинального процессов. В целом, в тех странах, где исследование начали в 2020-2021 году отмечена устойчивая тенденция к росту уровня популяционного иммунитета (доли серопозитивных лиц) в ходе пандемии. А в тех странах которые подключились к исследованию в более поздний период развития пандемии в 2022 году значительная часть населения уже перенесла COVID-19 в манифестной или бессимптомной форме, поэтому не были выявлены статистически значимые возрастные, профессиональные и территориальные отличия в серопревалентности населения как вследствие интенсивного «проэпидемичивания», так и вследствие кампании по вакцинации, начавшейся в середине 2021 года. В первой половине 2021 г. и активно проводившаяся во всех странах вакцинация против коронавируса (как первичная, так и бустерная) стали главными причинами повышения уровня популяционного иммунитета. При этом в структуре серопозитивности произошел сдвиг в сторону увеличения доли лиц, имевших антитела только к RBD. На поздних сроках пандемии в 2022-2023 годах практически у 90% серопозитивных волонтёров гуморальный иммунитет был представлен антителами к обоим антигенам (Nc+RBD). Очевидно, что на поздних сроках пандемии в условиях высокой заболеваемости высоко трансмиссивным штаммом и высокого охвата вакцинацией популяционный иммунитет является «гибридным». The Russian Federation has been working consistently to assist partner countries in building scientific capacity and expanding co-operation in the study of infectious diseases. At the beginning of the COVID-19 pandemic, with the support of the Government of the Russian Federation, Rospotrebnadzor developed a multi-stage programme of seromonitoring of population immunity to SARS-CoV-2, which was implemented in the Russian Federation, the Kyrgyz Republic, the Republic of Belarus, the Republic of Armenia and the Republic of Tajikistan. Different age and professional groups of the countries were included in the studies. IgG antibody levels to two major SARS CoV2 antigens: nucleocapsid (Nc) and receptor-binding domain S-protein (RBD) were assessed in volunteers because of their maximal presence during the infection or postvaccination processes. In general, in those countries where the study began in 2020-2021, there was a steady trend towards increasing levels of population immunity (the proportion of seropositive individuals) during the pandemic. In those countries that joined the study later in the pandemic in 2022, a significant proportion of the population had already experienced COVID-19 in manifest or asymptomatic form, so there were no statistically significant age, occupational or geographic differences in seroprevalence due to both the intensive "pro-epidemic" and the vaccination campaign that began in mid-2021. In the first half of 2021, vaccination against coronavirus (both primary and booster), which was actively carried out in all countries, became the main reasons for the increase in the level of population immunity. At the same time, there was a shift in the structure of seropositivity towards an increase in the proportion of individuals who had antibodies only to RBD. At the late dates of the pandemic in 2022-2023, almost 90% of seropositive volunteers had humoral immunity represented by antibodies to both antigens (Nc+RBD). It is evident that population immunity is "hybrid" in the late pandemic, under conditions of high incidence of a highly transmissible strain and high vaccination coverage. Россия Федерациясы өнөктөш өлкөлөргө илимий потенциалды жогорулатууда жана жугуштуу ооруларды изилдөөдө кызматташтыкты кеңейтүүдө жардам көрсөтүү боюнча ырааттуу иш алып барууда. COVID-19 пандемиясынын башталышында Россия Федерациясынын Өкмөтүнүн колдоосу менен Роспотребнадзор калктын SARS-CoV-2ге каршы иммунитетине серомониторинг жүргүзүү боюнча көп этаптуупрограмманы иштеп чыккан, ал Россия Федерациясында, Кыргыз Республикасында, Беларусь Республикасында, Армения Республикасында жана Тажикстан Республикасында ишке ашырылган. Изилдөөлөр тизмеленген өлкөлөрдүн ар кандай курактагы жана кесипкөй топторун камтыган. Ыктыярчылар SARS CoV-2нин эки негизги антигенине IgG антителолорунун деңгээли боюнча бааланган: нуклеокапсид (Nc) жана S протеининин (RBD) рецепторду байланыштырган домени, алардын инфекциялык же эмдөөдөн кийинки процесстеринде максималдуу өкүлчүлүгүнө байланыштуу. Жалпысынан 2020-2021-жылдары изилдөө башталган өлкөлөрдө пандемия учурунда калктын иммунитетинин деңгээлинин (серопозитивдүү адамдардын үлүшү) жогорулашынын туруктуу тенденциясы байкалган. Ал эми 2022-жылы пандемиянын өнүгүшүнүн кийинки мезгилинде изилдөөгө кошулган өлкөлөрдө калктын олуттуу бөлүгү COVID-19дан манифесттик же симптомсуз түрдө ооруган, ошондуктан статистикалык маанилүү айырмачылыктар жаш курагы, кесиптик жана аймактык калктын, серопреваленттүүлүгү интенсивдүү “эпидемияга каршы” жана 2021-жылдын ортосунда башталган эмдөө өнөктүгүнүн натыйжасында аныкталган жок. 2021-жылдын биринчи жарымында бардык өлкөлөрдө активдүү жүргүзүлүп жаткан коронавируска каршы эмдөө (баштапкы да, бутер да) калктын иммунитетинин деңгээлинин жогорулашынын негизги себептери болуп калды. Ошол эле учурда,серопозитивдүүлүк структурасында RBDга гана антителолору бар адамдардын үлүшүнүн көбөйүшүнө карай жылыш болгон. 2022-2023-жылдардагы пандемиянын кийинки этаптарында серопозитивдүү волонтерлордун дээрлик 90% эки антигендерге (Nc+RBD) антителолор менен гуморалдык иммунитетке ээ болушкан. Пандемиянын кийинки этаптарында, өтө өтүүчү штаммдын пайда болушунун жана вакцинациянын жогорку камтылышынын шарттарында калктын иммунитети “гибриддик” экендиги айдан ачык.

Background. The COVID-19 pandemic has become a substantial global health crisis, unparalleled in world history. Infection dynamics can have specific characteristics in different countries due to social, economic, climatic, or geographic factors. Aim: to study features of SARS-CoV-2 collective immunity among the Armenian population. Materials and methods. A cross-sectional, randomized study of collective immunity was carried out according to a program developed by Rospotrebnadzor and the St. Petersburg Pasteur Institute, taking into account WHO recommendations. The study was approved by the ethics committees of the National Center for Infectious Diseases (Armenia) and the St. Petersburg Pasteur Institute (Russia). A volunteer cohort was formed (N = 6057), randomized by age and region. The studys analysis included: shares and distributions of antibodies (Abs) to nucleocapsid (Nc) antigen (Ag) and receptor binding domain (RBD) S-1 Ag in the cohort; and quantitative determination of these Abs by ELISA. During the survey, a history of vaccination was indicated by 4395 people. Results. Overall seropositivity formed in the whole cohort (by April 14, 2022) was 98.6% (95% CI: 98.198.7). It did not depend on age, place of residence, or occupation. When quantifying Nc and RBD Abs, the proportions of volunteers with Nc Ab levels of 117 BAU/ml and RBD Ab levels of 22.6220 BAU/ml were the smallest, amounting to 6.9% (95% CI: 6.27.5) and 20.4% (95% CI: 19.421.4), respectively. With increasing serum concentrations (Nc 667 BAU/ml, RBD 450 BAU/ml), the proportions of individuals with the corresponding levels were 20.2% for Nc (95% CI: 19.221.3) and 54.2% for RBD (95% CI: 52.955.5). Vaccination coverage was 72.6% (95% CI: 71.573.7). The most frequently used were Sinopharm/BIBP (32.4%), AZD1222 (22.3%), and Gam-COVID-Vac (21%). The remaining vaccines (CoronaVac, mRNA-1273, BNT162b2, CoviVac) were used by 24.3% of vaccinated individuals. When summing vaccines by platform, it was found that: vector vaccines were used in 40.34% (95% CI: 33.5742.39) of cases; whole-virion vaccines were used in 26.83% (95% CI: 24.7632.20); and mRNA vaccines were used in 6.33% (95% CI: 4.848.91). Conclusion. The epidemic situation in Armenia by April 2022 was characterized by a high level of collective immunity, independent of age or regional factors. Vector and whole-virion vaccines have been used most widely.

The ongoing coronavirus disease (COVID-19) pandemic over the past three years has caused close attention to the problem of herd immunity, which is understood as: "resistance to the spread of a contagious disease within a population or herd". Collective immunity is formed both as a result of infection (natural spread of the pathogen in a population of susceptible individuals) and as a result of the use of specific vaccines. During the COVID-19 pandemic, both mechanisms for the formation of collective immunity were realized. In the first wave, there was a natural formation of collective immunity to the virus following recoveries from COVID-19 caused by pandemic spread of SARS-CoV-2. Starting from December 2020, the widespread use of specific vaccines against SARS-CoV-2 began in the USA, Great Britain, China, Russia, and a number of other countries. This launched the process of post-vaccination collective immunity formation; its features have depended on the vaccine types implemented. Currently, in those countries where vaccination and revaccination of recovered patients is widely carried out, immunity is "hybrid" in nature. Several commonalities should be noted in the pandemic experience: a somewhat regular, periodic (wavelike) nature of the COVID-19 epidemic process; changes in pathogen genetics in variants in all countries; and expansive mass vaccination programs in many populations. From these, we can draw some conclusions about the general trend for all countries in the formation of collective immunity during the pandemic: At the beginning of the pandemic in 2020, overall population seroprevalence did not exceed 20%. Other findings were: the highest seroprevalence rates were noted in the children's age group; pronounced regional differences were revealed; and the highest indicators were noted among medical workers. Collective immunity developed as a result of infection or illness, and in the majority of seropositive volunteers, it was represented by antibodies to both antigens. At the height of the pandemic in the summer of 2021, population seroprevalence reached 50%. This was due to both a significant number of convalescents and the start of mass vaccination campaigns. In all countries, specific differences in seroprevalence (by age, region, profession) leveled out, leading to more uniformity. During this period, the formation of "hybrid" immunity is clearly prominent, and the proportion of individuals with antibodies to RBD alone increased (due to vaccination with vector vaccines). Later, mass vaccination, as well as involvement of most of the population in the epidemic process due to the emergence of the highly contagious Omicron strain, raised the level of collective immunity to 80-90%. This led to a sharp decrease in COVID-19 incidence in the second half of 2022 in all countries participating in the study. In the later stages of the pandemic (2022-2023), almost 90% of seropositive volunteers had hybrid immunity, reflected as antibodies to both antigens (Nc, RBD).

Introduction: The COVID-19 pandemic has become a serious challenge for humanity almost everywhere globally. Despite active vaccination around the world, the incidence proportion in different countries varies significantly as of May 2022. The reason may be a combination of demographic, immunological, and epidemiological factors. The purpose of this study was to analyze possible relationships between COVID-19 incidence proportion in the population and the types of SARS-CoV-2 vaccines used in different countries globally, taking into account demographic and epidemiological factors. Materials and methods: An initial database was created of demographic and immunoepidemiological information about the COVID-19 situation in 104 countries collected from published official sources and repository data. The baseline included, for each country, population size and density; SARS-CoV-2 testing coverage; vaccination coverage; incidence proportion; and a list of vaccines that were used, including their relative share among all vaccinations. Subsequently, the initial data set was stratified by population and vaccination coverage. The final data set was subjected to statistical processing both in general and taking into account population testing coverage. Results: After formation of the final data set (including 53 countries), it turned out that reported COVID-19 case numbers correlated most strongly with testing coverage and the proportions of vaccine types used, specifically, mRNA (V1); vector (V2); peptide/protein (V3); and whole-virion/inactivated (V4). Due to the fact that an inverse correlation was found between 'reported COVID-19 case numbers' with V2, V3, and V4, these three vaccine types were also combined into one analytic group, 'non-mRNA group' vaccines (Vnmg). When the relationship between vaccine type and incidence proportion was examined, minimum incidence proportion was noted at V1:Vnmg ratios (%:%) from 0:100 to 30:70. Maximum incidence proportion was seen with V1:Vnmg from 80:20 to 100:0. On the other hand, we have shown that the number of reported COVID-19 cases in different countries largely depends on testing coverage. To offset this factor, countries with low and extremely high levels of testing were excluded from the data set; it was then confirmed that the largest number of reported COVID-19 cases occurred in countries with a dominance of V1 vaccines. The fewest reported cases were seen in countries with a dominance of Vnmg vaccines. Conclusion: In this paper, we have shown for the first time that the level of reported COVID-19 incidence proportion depends not only on SARS-CoV-2 testing and vaccination coverage, which is quite logical, but probably also on the vaccine types used. With the same vaccination level and testing coverage, those countries that predominantly use vector and whole-virion vaccines feature incidence proportion that is significantly lower than countries that predominantly use mRNA vaccines.

Introduction. Since the detection of the first COVID-19 patient, 2 years have passed, during which more than 287,862,000 people have fallen ill globally, of which about 1.9% died. The implementation of SARS-CoV-2 control programs required efforts from almost all countries. An important direction in the fight against COVID-19 has been the formation of herd immunity, the main tool for managing the pandemic. Study goal. The aim of the study was to assess the seroprevalence of antibodies (Abs) to SARS-CoV-2 nucleocapsid (Nc) and receptor binding domain (RBD) in the St. Petersburg population during the COVID-19 pandemic. Materials and methods. A longitudinal cohort randomized monitoring study of Ab seroprevalence (SARS-CoV-2 Nc, RBD) was organized and conducted according to a unified methodology developed by Rospotrebnadzor with the participation of the St. Petersburg Pasteur Institute. For this purpose, a cohort was formed of 1000 volunteers who participated in all five stages of seromonitoring. The cohort was divided into seven age groups: 1–17; 18–29; 30–39; 40–49; 50–59; 60–69; 70; and older (70+) years. Seropositivity levels (Nc, RBD) were assessed by quantitative and qualitative enzyme immunoassays. During the second year of monitoring, some volunteers were vaccinated with the GamCOVIDVac (84%) or EpiVacCorona (11.6%) vaccines approved in Russia. Statistical processing was carried out using Excel 2010. Confidence intervals for shares and percentages (95% CI) were calculated using the method of A. Wald and J. Wolfowitz with adjustment (A. Agresti, B.A. Coull). The statistical significance of differences was calculated by z-test, using the appropriate online calculator (p < 0.05) unless indicated. Results. There was a trend toward an increase in Nc seropositivity in stages 1–3 of seromonitoring, with a decrease in stages 4–5 among children and adults. The share of RBD seropositive steadily increased during all five stages of seromonitoring. The most frequent finding was low anti-RBD Abs levels (22.6–220 BAU/mL). High Ab levels were recorded statistically significantly less frequently. Asymptomatic forms were observed in 84–88% of SARS-CoV-2 seropositive volunteers. By the fifth stage of monitoring, this indicator significantly decreased to 69.8% (95% CI: 66.1–73.4). The monitoring revealed a statistically significant increase in anti-RBD Abs alongside a statistically significant decrease in the proportion of Nc seropositives. This dynamic was especially characteristic of persons vaccinated with GamCOVIDVac. Conclusion. Prior to the use of specific vaccines, a seroprevalence of anti-Nc Abs was noted. After the introduction of the GamCOVIDVac vaccine in adults, a decrease in the level of anti-Nc Abs was noted due to an increase in the proportion of RBD seropositive persons.

In the fight against coronavirus infection, control of the immune response is of decisive importance, an important component of which is the seroprevalence of antibodies to SARS-CoV-2. Immunity to SARS-CoV-2 is formed either naturally or artificially through vaccination. The purpose of this study was to assess the seroprevalence of antibodies to SARS-CoV-2 in the population of Kyrgyzstan. A cross-sectional randomized study of seroprevalence was carried out according to a program developed by Rospotrebnadzor and the St. Petersburg Pasteur Institute, taking into account WHO recommendations. The ethics committees of the Association of Preventive Medicine (Kyrgyzstan) and the St. Petersburg Pasteur Institute (Russia) approved the study. Volunteers (9471) were recruited, representing 0.15% (95% CI 0.14-0.15) of the total population, randomized by age and region. Plasma antibodies (Abs) to the nucleocapsid antigen (Nag) were determined. In vaccinated individuals, Abs to the SARS-CoV-2 receptor-binding domain antigen (RBDag) were determined. Differences were considered statistically significant at p < 0.05. The SARS-CoV-2 Nag Ab seroprevalence was 48.7% (95% CI 47.7-49.7), with a maximum in the 60-69 age group [59.2% (95% CI 56.6-61.7)] and a minimum in group 1-17 years old [32.7% (95 CI: 29.4-36.1)]. The highest proportion of seropositive individuals was in the Naryn region [53.3% (95% CI 49.8-56.8)]. The lowest share was in Osh City [38.1% (95% CI 32.6-43.9)]. The maximum SARS-CoV-2 Nag seropositivity was found in the health-care sector [57.1% (95% CI 55.4-58.8)]; the minimum was seen among artists [38.6% (95% CI 26.0-52.4)]. Asymptomatic SARS-CoV-2 Nag seropositivity was 77.1% (95% CI 75.6-78.5). Vaccination with Sputnik V or Sinopharm produced comparable Ab seroprevalence. SARS-CoV-2 Nag seropositivity in the Kyrgyz population was 48.75% (95% CI 47.7-49.7), with the mass vaccination campaign undoubtedly benefitting the overall situation.

Abstract Introduction The COVID-19 pandemic that began in 2019 has become a serious challenge for humanity almost everywhere globally. Despite active vaccination around the world, prevalence in different countries varies significantly as of May 2022. The reason may be a combination of demographic, immunological, and epidemiological factors. The purpose of this study was to analyze the relationship between COVID-19 prevalence in the population and the types of SARS-CoV-2 vaccines used in different countries globally, taking into account demographic and epidemiological factors. Materials and methods An initial database was created of demographic and immunoepidemiological information about the COVID-19 situation in 104 countries, collected from published official source and repository data. The baseline included for each country: population size and density; SARS-CoV-2 testing coverage; vaccination coverage; prevalence; as well as a list of vaccines that were used, including their relative share among all vaccinations. Subsequently, the initial data set was stratified by population and vaccination coverage. The final data set was subjected to statistical processing both in general and taking into account population testing coverage. Results After formation of the final data set (including 53 countries), it turned out that reported COVID-19 case numbers correlated most strongly with testing coverage and the proportions of vaccine types used, specifically: mRNA (V1); vector (V2); peptide/protein (V3); and whole-virion/inactivated (V4). Due to the fact that an inverse correlation was found between 'reported COVID-19 case numbers' with V2, V3 and V4, these three vaccine types were also combined into one analytic group, 'non-mRNA group' vaccines (Vnmg). When the relationship between vaccine type and prevalence was examined, minimum prevalence was noted at V1:Vnmg ratios (%:%) from 0:100 to 30:70. Maximum prevalence was seen with V1:Vnmg from 80:20 to 100:0. On the other hand, we have shown that the number of reported COVID-19 cases in different countries largely depends on testing coverage. To offset this factor, countries with low and extremely high levels of testing were excluded from the data set; it was then confirmed that the largest number of reported COVID-19 cases occurred in countries with a dominance of V1 vaccines. The fewest reported cases were seen in countries with a dominance of Vnmg vaccines. Conclusion In this paper, we have shown for the first time that the level of reported COVID-19 prevalence depends not only on SARS-CoV-2 testing and vaccination coverage, which is quite logical, but also on the vaccine types used. With the same vaccination level and testing coverage, those countries that predominantly use vector and whole-virion vaccines feature prevalence that is significantly lower than countries that predominantly use mRNA vaccines.

Objective: to study the seroprevalence of SARS-CoV-2 antibodies (AB) in children in the 2nd year of the COVID-19 pandemic in Russia. Materials and methods: prospective cohort study. The seroprevalence research was conducted among 3670 children aged 1 to 17 y/o from 26 modelling regions of Russia (that have been participating earlier in the five stages of seromonitoring during 2020-2021). The serological testing was carried out in December, 2021. The work was carried out according to a unified methodology set by the Russian Federal Service for Supervision of Consumer Rights Protection and Human Well-Being with the Pasteur Institute of Epidemiology and Microbiology (Saint Petersburg, Russia). The plasma was obtained from 3 ml of venous blood, in which the level of AB to nucleocapsid (NC), and the SARS-CoV-2 receptor-binding domain (RBD) was determined by immunoferment method using reagents for qualitative and quantitative analysis. Results: the analysis of AB seroprevalence to NC and RBD showed the statistically significant increase in the share of seropositivity to RBD in children of all modelling regions (p<0.05). The most seropositive volunteers contained low levels of AB: 31.3-125.6 BAU/ml NC and 22.6-220 BAU/ml RBD. An increase in the level of AB to NC and RBD was accompanied by a decrease in the percentage of seropositive patients. Evaluating the contribution of children to the level of humoral immunity, convalescents (had been ill shortly before the examination), the “anamnesis” (had been ill at previous stages of seromonitoring) and asymptomatic (had been asymptomatically ill) groups were distinguished. The maximum contribution was made by children with asymptomatic cases of COVID-19 in anamnesis: in 82.3% (95% CI 81.1-83.6), of which 76.9% (95% CI 75.5-78.3) AB detected to RBD. The contribution of children of two other groups to the overall level of humoral immunity was 33 times less. Conclusion: statistically significant predominance of AB to RBD above AB to NC and their main contribution to the level of humoral immunity to SARS-CоV-2 (p<0.001).

The aim: to study the structure and dynamics of population immunity to SARSCoV-2 of the population of the Southern Regions of the Far East (SRFE): Khabarovsk, Primorsky Krai and Amur Region during the COVID-19 epidemic in 2020.Materials and methods. The work was carried out according to the program for assessing population immunity to SARS -CoV-2 of the population of the Russian Federation according to the methodology developed by the Rospotrebnadzor with the participation of the St. Petersburg Pasteur Institute. The study was approved by the ethical committee of the St. Petersburg Pasteur Institute. The selection of participants was carried out by a questionnaire method using cloud technologies. The volunteers were randomized by age by stratification into 7 age groups: 1–17, 18–29, 30–39, 40–49, 50–59, 60–69, 70+ years old. Territorial randomization consisted in limiting the engaging of volunteers – no more than 30 people from one enterprise. After the initial cross-sectional study, a 3-stage seromonitoring was carried out, in which the same volunteers participated. Antibodies to the SARS-CoV-2 nucleocapsid were determined in peripheral blood serum by the enzyme immunoassay using an appropriate set of reagents produced by the State Scientific Center for Medical and Biological Sciences of the Rospotrebnadzor (Obolensk). Statistical analysis was performed using the Excel package. The confidence interval for the proportion was calculated using the A. Wald, J. Wolfowitz method with A. Agresti, B.A. Coull’s correction. The statistical significance of the differences was calculated online using a specialized calculator. The statistical significance of the differences was assessed with a probability of p˂ 0.05, unless otherwise indicated.Results. In a comparative analysis, the highest morbidity was observed in the Khabarovsk Territory, the lowest – in the Primorsky Territory. The level of seroprevalence among the population of the region was 19.6 % (95 % CI: 18.2–21.1) in the Khabarovsk Territory, 19.6 % (95 % CI: 18.1–21.2) in the Primorsky Territory19,6 % and 45,5 % (95 % CI: 43.7–47.3) in the Amur region. The highest seroprevalence was noted among 1–17 years old children, mainly due to the subgroup of 14–17-years-olds. The smallest proportion of seropositive was found among 40–49-year-olds in the Khabarovsk Territory (14.7 %, 95 % CI: 11.2–18.6), 18–28-yearolds in the Primorsky Territory (13.3 %, 95 % CI: 10.0–17.1) and 30–39-year-olds in the Amur Region (36.3 %, 95% CI: 31.7–41.6). No statistically significant dependence of seroprevalence on territorial and occupational factors has been established, with the exception of an increase in the proportion of seropositive medical workers in Primorsky Territory. In the process of 3-stage seromonitoring, a regular increase in the proportion of seropositive people was revealed in all SRFE. The resulting tendency is correctly described by a second-order polynomial. A relationship was revealed between the number of convalescents and persons in contact with them, which made it possible to calculate the base reproductive number (R0) in the range from 1.4 (Primorsky Territory) to 2.4 (Amur Region). Analysis of seroprevalent volunteers showed that the number of asymptomatic individuals varied from 94.1 % (95 % CI: 92.8–95.3) to 98.3 % (95 % CI: 98.8–99.2). This indicates that most of the volunteers had COVID-19 asymptomatically.Conclusions. A comparative study showed the prevalence of seroprevalence in the Amur Region compared with the Khabarovsk and Primorsky Territories. The relationship between the number of convalescents and persons in contact with them was noted. The value of the base R0 is calculated. It has been shown that more than 90 % of seropositive individuals in the COVID-10 SRFE were asymptomatic.

By August 2020, more than 850000 cases of new coronavirus infection (COVID-19) caused by SARSCoV-2 were confirmed in the Russian Federation, with the Rostov Region as one of the ten most affected regions in Russia. The spread of the disease is largely determined by the state of population immunity in a certain area. Our research focuses on specific humoral immune response and estimates the level of herd immunity to SARS-CoV-2 virus among the population of the Rostov Region.Materials and methods. The study involved 3,048 people; the volunteers participating in the study were divided into seven age groups. The content of antibodies to SARS-CoV-2 was determined applying ELISA using a kit for the analysis of human serum or blood plasma for the presence of specific IgG to the nucleocapsid of the SARS-CoV-2 virus, manufactured by the State Scientific Center of Applied Microbiology and Biotechnology (Obolensk) in accordance with the instructions for use.Results and discussion. The assessment of seroprevalence to SARS-CoV-2 in the Rostov Region showed that the proportion of people positive for IgG to the new coronavirus was 16.5 %, the range of seropositive individuals in the general population was between 13.9 % and 19.1 % (p<0.05). There were no significant gender differences in the degree of seroprevalence with a positive result registered in 16.6 % of women and 16.5 % of men. A high level of humoral immunity to SARS-CoV-2 was established in individuals aged 1–17 against the background of low incidence rates, which may indicate the dominance of asymptomatic forms of the disease in this age group. The highest level of seropositivity was found in preschool children (33.6 %), students (29.3 %), employees (17.3 %), and education professionals (15.3 %).